Cleaning tool and a method for treating an inner surface of a casing

ABSTRACT

The present invention relates to a cleaning tool for cleaning and treating an inner surface of a downhole casing. The cleaning tool comprises a tool housing, a mechanical cleaning tool section comprising mechanical cleaning elements for releasing elements of the inner surface of the casing in order to clean the casing to become substantially free from rigid debris and other precipitated materials, and a jetting tool section for ejecting an enzyme-containing fluid onto the cleaned inner surface. The jetting tool section comprises a fluid chamber comprising the enzyme-containing fluid, and a nozzle head comprising at least one nozzle. The invention further relates to a method for treating an inner surface of a casing by means of the cleaning tool.

FIELD OF THE INVENTION

The present invention relates to a cleaning tool for cleaning andtreating an inner surface of a downhole casing and to a method fortreating an inner surface of a casing by means of the cleaning tool.

BACKGROUND ART

Downhole borehole operations are becoming more and more sophisticatedwith regard to tool operations, but also with regard to the complexityof borehole casing parts, such as valves, sliding sleeves, productionzones, etc. This increased complexity results in an increased demand forsolutions as to how to avoid undesirable effects, such as corrosion andfouling of the borehole casing parts. Chemical incrustation is a majorcause of decreased well performance and eventual failure. Fouling can bedescribed as clogging and failure of mechanical downhole parts, e.g. dueto creation of scale, debris or similar elements. The effect of theprecipitating and depositing of minerals can plug and close valves andsliding sleeves within a relatively short period of time. Hence, a needexists for an effective method for avoiding corrosion, depositing orfouling in downhole environments.

SUMMARY OF THE INVENTION

It is an object of the present invention to wholly or partly overcomethe above disadvantages and drawbacks of the prior art. Morespecifically, it is an object to provide a tool for cleaning a well anda method of preventing fouling which are cheaper and less toxic thantools and methods associated with chemical cleaning.

The above objects, together with numerous other objects, advantages, andfeatures, which will become evident from the below description, areaccomplished by a solution in accordance with the present invention by acleaning tool for cleaning and treating an inner surface of a downholecasing, comprising:

-   a tool housing,-   a mechanical cleaning tool section comprising mechanical cleaning    elements for releasing elements of the inner surface of the casing    in order to clean the casing to become substantially free from rigid    debris and other precipitated materials, and-   a jetting tool section for ejecting an enzyme-containing fluid onto    the cleaned inner surface, comprising:    -   a fluid chamber comprising the enzyme-containing fluid, and    -   a nozzle head comprising at least one nozzle.

In an embodiment, the jetting tool may comprise a pumping device forpressurising the fluid before the fluid is let out through the nozzlehead.

In another embodiment, the cleaning tool may further comprise an inletfor letting well fluid into the tool.

In a third another embodiment, the cleaning tool may further comprise amixing chamber for mixing the well fluid with the enzyme-containingfluid before the fluid is ejected out through the nozzle head.

In a fourth embodiment, the cleaning tool may further comprise aflow-hindering element arranged outside the housing, expandable againstthe inner surface of the casing so as to divide the casing into a firstcasing part and a second casing part.

The flow-hindering element may be a sweeper sweeping the inner surfaceof the casing after the mechanical cleaning tool section has releasedelements of the inner surface.

Furthermore, the cleaning tool may further comprise a sweeper sweepingthe inner surface of the casing after the mechanical cleaning toolsection has released elements of the inner surface.

Moreover, the mechanical cleaning elements may be brushes.

In an embodiment, the cleaning tool as described above may furthercomprise an inlet for letting well fluid into the tool, which inlet isin fluid communication with the nozzle through a valve so as to cleanthe inner surface before the inner surface is treated withenzyme-containing fluid.

Furthermore, the nozzle head may be extendable radially from the toolhousing for contacting the inner surface of the casing with theenzyme-containing fluid.

Additionally, the jetting tool may further comprise a hydraulic controlunit for controlling rotation of the nozzle head.

Having a hydraulic control unit for controlling which nozzles areejecting fluid ensures that the nozzles not facing the object to becleaned are not ejecting fluid and that all the pressure in the fluid isused for ejecting fluid through the nozzle/nozzles facing the object tobe cleaned. Thus, no energy of the pressurised fluid is wasted onnozzles not facing the object to be cleaned, and/or no energy is wastedon rotating the nozzle head. Furthermore, by controlling whichnozzle/nozzles is/are allowed to eject fluid, it is possible to ensurethat only one or few of the nozzles is/are in fact ejecting fluid, andthe pressure of the fluid ejected from that or those nozzles is thussignificantly higher than if the fluid was ejected through all thenozzles at the same time, even if the object to be cleaned is extendingalong the entire circumference of the casing. In this way, each nozzleis able to clean harder materials, such as scales, than nozzles of priorart tools where most of the energy of the pressurised fluid is used forrotating the nozzles.

In one embodiment, the hydraulic control unit may comprise a motor forbreaking the free rotation of the nozzle head.

Moreover, the mechanical cleaning tool section may comprise a pumpingdevice for pumping fluid containing elements released by the brushes andejecting the fluid through an outlet of a first end or second end of thecleaning tool.

The cleaning tool as described above may further comprise a coating toolsection for coating the inner surface of the casing.

Furthermore, the coating tool section may comprise a brush arranged on aprojectable brush arm and wherein coating is ejected through openings inthe brush and the brush arm is rotated around a tool axis for contactingan inner surface of the casing with the coating.

Also, the cleaning tool as described above may further comprise adriving unit for propelling the tool forward in the casing.

Additionally, the tool may further comprise a wax fluid chambercomprising fluid containing wax particles.

In an embodiment, the wax particles may comprise ceramic particleshaving a significantly higher density than the wax.

Furthermore, the wax particles may comprise magnetic particles, and thewax particles comprising magnetic particles may be retained near thecasing wall due to magnetic attraction between the casing and themagnetic particles.

Said inner surface may be comprised in an oil and gas well drillingsystem.

The present invention furthermore relates to a method for treating aninner surface of a casing by means of the cleaning tool according to anyof the preceding claims, wherein the contact of the inner surface of thedownhole casing with an enzyme comprises the steps of:

-   providing an enzyme-containing fluid in the fluid chamber of the    jetting tool,-   cleaning the casing to remove rigid debris and other precipitated    materials, such as scales, by applying a mechanical cleaning tool    section comprising brushes for brushing the inner surface of a    casing downhole in order to clean the casing to become substantially    free from any elements, such as rigid debris and other precipitated    materials,-   jetting the fluid through the nozzle head towards the inner surface    of the casing in a jet stream, and-   contacting the inner surface of the casing with the    enzyme-containing fluid in a jet stream.

Moreover, the contact of the inner surface of the downhole casing withan enzyme may comprise the steps of providing a fluid containing enzymesin a fluid chamber of a jetting tool, activating a pumping device in thejetting tool and pressurising the fluid chamber of the jetting tool,jetting the fluid through a nozzle head towards the inner surface of thecasing in a jet stream, and contacting the inner surface of the casingwith an enzyme in a jet stream.

Further, the fluid chamber may be cooled. Since the activity of theenzymes may be deteriorated by elevated temperatures, the fluid chambercontaining enzymes may be cooled to below a critical temperature, suchthat all enzymes are viable when applied downhole in the borehole.Temperature fluctuations downhole may be caused by various differenteffects, such as high temperature fluids flowing past the tool, hightemperature regions of the formation, e.g. due to proximity of magmalayers, explosions during perforations and so on. Therefore, temperaturecontrol of the fluid chamber may help avoid damages to the enzymesdownhole.

Moreover, the method as described above may further comprise a finalstep of arranging a wax layer on the inner surface of the casing, themethod comprising the steps of providing a fluid containing waxparticles in a first casing part, activating a pumping device andpressurising the first casing part, jetting the fluid containing waxparticles through the nozzle head towards the inner surface of thecasing in the second casing part in a jet stream, and arranging the waxlayer on the inner surface of the casing by the jet stream.

In one embodiment, the particles may be made of metal.

The method as described above may further comprise a final step ofarranging a layer of nanoparticles on the inner surface of the casing,comprising the steps of providing a liquid containing nanoparticles in afirst casing part, activating a pumping device and pressurising thefirst casing part, jetting the liquid through a nozzle head towards theinner surface of the casing in the second casing part in a jet stream,and arranging the layer of nanoparticles on the inner surface of thecasing by the jet stream.

In addition, the method as described above may further comprise aninitial step of preparing surfaces of downhole casing parts, such ascasings, pipes, tubes, valves, plugs and collars, which may come intocontact with borehole fluids, comprising the steps of coating an innersurface of a casing part with a nanocover material, and mounting thecoated casing part to the casing.

Finally, the method as described above may further comprise a step ofpreparing surfaces of downhole casing parts, such as casings, pipes,tubes, valves, plugs and collars, which may come into contact withborehole fluids, comprising the steps of lowering a coating tool intothe borehole, and coating at least a surface of a casing part with ananocover material.

In one embodiment, the nanocover material may be graphene.

Moreover, the nanocover may be below 500 nanometers in thickness, suchas below 100 nm, such as below 50 nm, such as below 20 nm, such as below10 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its many advantages will be described in more detailbelow with reference to the accompanying schematic drawings, which forthe purpose of illustration show some non-limiting embodiments and inwhich

FIG. 1 shows a partly cross-sectional view of a tool according to theinvention,

FIG. 2 shows another embodiment of the tool having brushes for cleaningan inner surface of a borehole casing,

FIG. 3 shows another embodiment of the tool having a jetting toolsection for cleaning the inner surface of the borehole casing,

FIG. 4 shows yet another embodiment of the tool for cleaning the innersurface of the borehole casing,

FIG. 5 shows an embodiment of the tool arranged in a section of theborehole casing comprising a mechanical sliding sleeve,

FIG. 6 shows yet another embodiment of the tool,

FIG. 7 shows yet another embodiment of the tool, and

FIG. 8 shows yet another embodiment of the tool for cleaning and coatingthe inner surface of the borehole casing.

All the figures are highly schematic and not necessarily to scale, andthey show only those parts which are necessary in order to elucidate theinvention, other parts being omitted or merely suggested.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a cleaning tool 1 for inhibitingcorrosion or degrading of a downhole casing 2 by hindering scale 5 beingdeposited on an inner surface of the casing. FIG. 1 shows how anenzyme-containing fluid 4 is ejected from an ejecting member 6 ornozzles 13 comprised in a nozzle head 16 of the cleaning tool 1. Byejecting the enzyme-containing fluid 4 towards the inner surface 3 ofthe borehole casing 2, the enzymes come into contact with the innersurface 3. To hinder any future deposits of scale 5 or similar layers onthe inner surface, the enzyme-containing fluid 4 needs to contact aclean surface, and to this effect, an initial cleaning step of releasingthe rigid scale or debris and other deposit materials may be carriedout. This cleaning step may be performed by a mechanical cleaning toolsection 30 comprising mechanical cleaning elements 23 for releasingelements, such as scales, of the inner surface of the casing 2. Themechanical cleaning tool section 30 is connected with the nozzle head 16so that when the cleaning tool 1 moves forwards or backwards in thewell, the mechanical cleaning tool section 30 releases the scale ordebris of the inner surface 3, and subsequently, the enzyme-containingfluid 4 is ejected from the nozzle head 16 to contact the cleanedsurface. Thus, if the cleaning tool 1 is retracted while cleaning andtreating the casing, the mechanical cleaning tool section 30 is arrangedclosest to the top of the well, as shown in FIG. 2, and if the cleaningtool is moving forward while cleaning and treating the casing, thenozzle head 16 is arranged closest to the top of the well, as shown inFIG. 1.

As shown in FIG. 1, the tool further comprises a jetting tool section 17for contacting the inner surface of the downhole casing with an enzyme.The fluid containing enzymes 4 is contained in a fluid chamber 7 of thejetting tool 17, and after pressurising the chamber 7, either by apumping device 9 downhole pressurising locally in the jetting toolchamber 7 or by a pumping device uphole (not shown), e.g. pressurisingthe entire borehole casing above the jetting tool 17, the fluid 4containing enzymes may be jetted through the nozzle head 16 towards theinner surface 3 of the casing in a jet stream, thereby contacting theinner surface of the casing with an enzyme in the jet stream.

A mechanical cleaning tool section 30 for carrying out theabove-mentioned mechanical cleaning using brushes 23 is shown in FIG. 1.The mechanical cleaning tool section 30 may comprise brushes 23 forbrushing the interior of the casing downhole in order to clean thecasing to become substantially free from rigid debris and otherprecipitated materials. In another embodiment, the initial step ofcleaning the casing to remove rigid debris and other deposit materials,such as scales, may alternatively be carried out by another mechanicalcleaning tool section 30 in the form of the jetting tool section 17, asshown in FIG. 3. The jetting tool 17 may be very powerful in removingeven rigid debris and other precipitated materials strongly attached tothe inner surface of the borehole.

Scale is formed downhole by constituents from the formation and/or fromfluid injected into the well. Scale tends to deposit on the innersurface of the casing in a heterogeneous reaction, but by applyingenzymes onto the clean inner surface 3, the enzymes react with the scaleconstituents, causing the scale to form as a homogeneous reaction ratherthan a heterogeneous reaction. The enzymes thus promote a homogeneousreaction where the scale precipitates in the fluid and does not depositon the inner surface of the casing. The enzymes for promoting ahomogeneous reaction may be ligases.

FIG. 2 shows the cleaning tool 1 comprising a tool housing 14 and aninlet 15 for letting well fluid into the tool 1, and the inlet 15 isarranged inside the tool in fluid communication with the nozzles 13, asillustrated by the dotted lines. The well fluid travels in through theinlet and out through the nozzle head 16, as illustrated by arrows. Thewell fluid is mixed with the enzyme-containing fluid 4 inside thecleaning tool before being ejected onto the nozzle head 16. The cleaningtool is submerged into the casing 2 in the well, and a flow-hinderingelement 8 arranged outside the housing 14 is set or inflated so that itdivides the casing 3 into a first 20 and a second casing part 21.Thereby, the well fluid in the first casing part 20 can be pressurised,and the fluid is forced into the inlets 15 and out through the nozzles13. Thus, the second part of the casing 21 has a substantially lowerwell fluid pressure so that the high-pressurised well fluid in the firstpart 20 can be ejected as jets in the well fluid in the second part ofthe casing. The flow-hindering element 8 also has the function ofsweeping the inner surface 3 of the casing 2 after the mechanicalcleaning tool section 30 has released the scales 5 as the tool 1 ismoved forward in the well, forward being downwards in FIG. 2. Theflow-hindering element is thus also functioning as a sweeper.

In FIG. 3, the cleaning tool 1 is also submerged into the casing 3 inthe well, and the flow-hindering element 8 is arranged outside thehousing 14, dividing the casing 3 into the first 20 and the secondcasing part 21. The well fluid in the first casing part 20 ispressurised, and the fluid is forced into the inlets 15 and out throughthe nozzles 13 in the jetting tool section 17 for cleaning the surface3. The well fluid jetted through the jetting tool section 17 is notmixed with the fluid for cleaning the inner surface, as a valve directspart of the fluid into the jetting tool section and not through thechamber. In some embodiments, the cleaning fluid may therefore be fluidfrom the casing jetted through the nozzles, and not a special cleaningfluid contained in a fluid chamber in the jetting tool section 17. Theother part of the fluid is directed into the mixing chamber to be mixedwith the enzyme-containing fluid 4 and ejected through the nozzle head16 to contact the clean inner surface with enzymes. The sweeper 10arranged between the jetting tool section 17 and the nozzle head 16sweeps the inner surface from released scale 5 before the surface iscontacted by enzymes.

The cleaning tool of FIG. 3 further comprises a hydraulic control unit18 for controlling rotation of the nozzle head. The jetting tool sectionmay in a similar manner comprise a hydraulic control unit 18 forcontrolling the nozzle head of the jetting tool section 17. Thehydraulic control unit may comprise an electric motor for breaking thefree rotation of the nozzle head. Having a hydraulic control unit forcontrolling which nozzles are ejecting fluid ensures that the nozzlesnot facing the object to be cleaned are not ejecting fluid and that allthe pressure in the fluid is used for ejecting fluid through the nozzleor nozzles facing the object to be cleaned. Thus, no energy of thepressurised fluid is wasted on nozzles not facing the object to becleaned, and/or no energy is wasted on rotating the nozzle head.Furthermore, by controlling which nozzle/nozzles is/are allowed to ejectfluid, it is possible to ensure that only one or few of the nozzlesis/are in fact ejecting fluid, and the pressure of the fluid ejectedfrom that or these nozzles is thus significantly higher than if thefluid was ejected through all the nozzles at the same time, even if theobject is extending along the entire circumference of the casing. Inthis way, each nozzle is able to clean harder materials, such as scales,than nozzles of prior art tools where most of the energy of thepressurised fluid is used for rotating the nozzles.

In FIG. 4, the pumping device 9 pumps fluid into the tool 1, which fluidis subsequently mixed with enzymes from the chamber 7 in the mixingchamber 11 before being ejected through the nozzle head 16.

Scale may cause clogging or malfunction of a mechanical device, such asa sliding sleeve downhole. Scale depositing on mechanical devices may beinhibited by contacting the mechanical device with an enzyme-containingfluid by means of the tool 1, as shown in FIG. 5. The sliding sleeve 19and the inner surface 3 of the casing are cleaned by brushes which aremade of cut plates but may in another embodiment be made of wiresextending radially outwards, as shown in FIG. 6. The mechanical cleaningtool section of FIG. 5 comprises a pumping device 9 for pumping fluidcontaining elements released by the brushes and ejecting the fluidthrough an outlet 22 of a first end 24 or second end 25 of the cleaningtool.

As shown in FIG. 7, the nozzle head 16 is extendable radially from thetool housing for contacting the inner surface of the casing with theenzyme-containing fluid. In FIG. 6, the nozzle head 16 is in itsretracted position, and in FIG. 7, the nozzle head 16 is in itsprojected position, extending radially outwards from the tool axis. Thecleaning tool 1 of FIGS. 6 and 7 comprises two driving units 26 poweredby wireline 27 for propelling the tool forward in the casing.

In FIG. 7, the cleaning tool further comprises a coating tool section 28for coating the inner surface of the casing. In FIG. 8, the coating toolsection 28 comprises a brush 31 arranged on a projectable brush arm 32,and coating is ejected through openings in the brush while the brush armis rotated around a tool axis 40 for contacting the inner surface 3 ofthe casing 2 with the coating. The brush thus coats the cleaned innersurface of the casing before the enzyme-containing fluid 4 is ejected tocontact the inner surface.

The tool may further comprise a wax fluid chamber comprising fluidcontaining wax particles which, like the coating, is applied to thesurface of the casing before the casing is treated with enzymes. The waxparticles may comprise ceramic particles having a significantly higherdensity than the wax so that the wax particles may be ejected throughnozzles or ejecting members 6 to contact the inner surface of thecasing. The wax particles may also comprise magnetic particles, and theejected wax particles comprising magnetic particles are thus retainednear the casing wall due to magnetic attraction between the casing andthe magnetic particles.

The enzyme-containing fluid may also contain wax, adhesive or similarconstituents to be able to adhere to the inner surface. The enzymes arethen slowly “washed off” or “abraded” and mixed with the well fluid topromote a homogeneous reaction, and scales are thus formed in the wellfluid and drops to the bottom of the well in a vertical well.

The nozzles of the nozzle head may be angled in relation to a radialdirection of the nozzle head being perpendicular to the tool axis. Thenozzles are arranged in rows and along a circumference of the nozzlehead with a mutual circumferential distance. By angling the nozzles, therotation of the nozzle head is provided by the pressurised fluid.

Due to elevated downhole temperatures, enzymes are preferablythermophile or hyperthermophile in order to withstand temperatures above50 degrees Celsius, such as above 60 degrees Celsius, such as above 70degrees Celsius, such as above 80 degrees Celsius, such as above 90degrees Celsius, such as above 100 degrees Celsius, such as above 110degrees Celsius, such as above 120 degrees Celsius, such as above 130degrees Celsius, such as above 140 degrees Celsius, such as above 150degrees Celsius, such as even above 200 degrees Celsius.

As known from examples such as an ordinary carwash, a wax layer may bearranged on a cleaned surface to extend the period of maintaining aclean surface and to inhibit corrosion effects. Applying wax to asurface in a downhole environment is, however, a much more difficulttask due to the nature of the downhole environment being a casing filledwith various fluids, e.g. drilling muds, oil, water, acid, etc.Therefore, application of a light and relatively volatile substance,such as a wax, is quite difficult. However, by injecting wax particlesinto a pressurised fluid chamber of the jetting tool section 17 andsubsequently ejecting them towards the inner surface of the boreholecasing in a jet stream may enable the user to arrange a layer of wax onthe inner surface.

Furthermore, experiments have shown that in very troublesome conditions,such as during high fluid flow rates in the borehole casing, very goodresults have been obtained by encapsulating relatively heavy ceramicparticles, such as aluminium oxide particles encapsulated in wax,thereby constituting a ceramic carrier material and ejecting thesewax-encapsulated ceramic particles towards the inner surface of theborehole casing. These wax-encapsulated ceramic particles are much moreeasily directed through a flowing fluid, such as by the jetting stream,in order to reach the inner surface of the borehole casing or othermechanical parts, preferably to be covered by a wax layer after cleaningand application of enzyme since the density of the wax may besignificantly increased by the ceramic carrier material. The particlesmay also be made of another suitable material, such as metals, alloys,etc.

Furthermore, experiments have also shown that extension of the periodwherein the surface is clean by applying a wax layer may be prolonged byadding magnetic particles also encapsulated by wax to increase adherenceto the inner surface of the borehole casing by magnetic attractionbetween particles and casing, when the casing is magnetic.

Other materials such as nano-scaled materials, e.g. self-assemblingnanotube layers, graphene layers, nano-crystalline thin films, etc., maybe used to cover the inner surface of the borehole casing or mechanicalcasing parts, such as sliding sleeves, in order to avoid or inhibitrigid debris, precipitated materials and scale. The nano-scaledmaterials may be applied to the casing components before mounting thecasing parts in the borehole or before the nano-scaled materials areapplied downhole by a downhole tool, such as a jetting tool section. Thenano-scaled materials may comprise enzymes diffusing slowly to thesurface facing the well fluid in the casing and thus mixing with thewell fluid.

The preparation of casing part surfaces may include application ofnano-scaled materials on pipes, tubes, valves, plugs, collars which maycome into contact with borehole fluids.

By well fluid is meant any kind of fluid that may be present in oil orgas wells downhole, such as natural gas, oil, oil mud, crude oil, water,etc. By gas is meant any kind of gas composition present in a well,completion, or open hole, and by oil is meant any kind of oilcomposition, such as crude oil, an oil-containing fluid, etc. Gas, oil,and water fluids may thus all comprise other elements or substances thangas, oil, and/or water, respectively.

By a casing is meant any kind of pipe, tubing, tubular, liner, stringetc. used downhole in relation to oil or natural gas production.

In the event that the tool is not submergible all the way into thecasing, a downhole tractor can be used to push the tool all the way intoposition in the well. The downhole tractor may have projectable armshaving wheels, wherein the wheels contact the inner surface of thecasing for propelling the tractor and the tool forward in the casing. Adownhole tractor is any kind of driving tool capable of pushing orpulling tools in a well downhole, such as a Well Tractor®.

Although the invention has been described in the above in connectionwith preferred embodiments of the invention, it will be evident for aperson skilled in the art that several modifications are conceivablewithout departing from the invention as defined by the following claims.

1. A cleaning tool (1) for cleaning and treating an inner surface (3) ofa downhole casing (2), comprising: a tool housing (14), a mechanicalcleaning tool section (30) comprising mechanical cleaning elements forreleasing elements of the inner surface of the casing in order to cleanthe casing to become substantially free from rigid debris and otherprecipitated materials, and a jetting tool section (17) for ejecting anenzyme-containing fluid onto the cleaned inner surface, comprising: afluid chamber (7) comprising the enzyme-containing fluid, and a nozzlehead (16) comprising at least one nozzle (13).
 2. A cleaning toolaccording to claim 1, wherein the jetting tool comprises a pumpingdevice (9) for pressurising the fluid before the fluid is let outthrough the nozzle head.
 3. A cleaning tool according to claim 1 or 2,further comprising a flow-hindering element (8) arranged outside thehousing (14), expandable against the inner surface of the casing so asto divide the casing (3) into a first casing part (20) and a secondcasing part (21).
 4. A cleaning tool according to claim 3, wherein theflow-hindering element is a sweeper (10) sweeping the inner surface ofthe casing after the mechanical cleaning tool section has releasedelements of the inner surface.
 5. A cleaning tool according to any ofthe preceding claims, wherein the mechanical cleaning elements arebrushes (23).
 6. A cleaning tool according to any of the precedingclaims, further comprising an inlet (15) for letting well fluid into thetool (1), which inlet is in fluid communication with the nozzle througha valve (12) so as to clean the inner surface before the inner surfaceis treated with enzyme-containing fluid.
 7. A cleaning tool according toany of the preceding claims, wherein the nozzle head is extendableradially from the tool housing for contacting the inner surface of thecasing with the enzyme-containing fluid.
 8. A cleaning tool according toany of the preceding claims, wherein the jetting tool further comprisesa hydraulic control unit (18) for controlling rotation of the nozzlehead.
 9. A cleaning tool according to any of the preceding claims,wherein the mechanical cleaning tool section comprises a pumping devicefor pumping fluid containing elements released by the brushes andejecting the fluid through an outlet (22) of a first end (24) or secondend (25) of the cleaning tool.
 10. A cleaning tool according to any ofthe preceding claims, further comprising a coating tool section (28) forcoating the inner surface of the casing.
 11. A cleaning tool accordingto any of the preceding claims, further comprising a driving unit (26)for propelling the tool forward in the casing.
 12. A method for treatingan inner surface of a casing by means of the cleaning tool according toany of the preceding claims, wherein the contact of the inner surface ofthe downhole casing with an enzyme comprises the steps of: providing anenzyme-containing fluid in the fluid chamber of the jetting tool (17),cleaning the casing to remove rigid debris and other precipitatedmaterials, such as scales, by applying a mechanical cleaning toolsection comprising brushes for brushing the inner surface of a casingdownhole in order to clean the casing to become substantially free fromany elements, such as rigid debris and other precipitated materials,jetting the fluid through the nozzle head towards the inner surface ofthe casing in a jet stream, and contacting the inner surface of thecasing with the enzyme-containing fluid in a jet stream.
 13. A methodaccording to claims 12, further comprising a final step of arranging awax layer on the inner surface of the casing, comprising the steps of:providing a fluid containing wax particles in a first casing part,activating a pumping device and pressurising the first casing part,jetting the fluid containing wax particles through the nozzle headtowards the inner surface of the casing in the second casing part in ajet stream, and arranging the wax layer on the inner surface of thecasing by the jet stream.
 14. A method according to claim 12 or 13,further comprising a final step of arranging a layer of nanoparticles onthe inner surface of the casing, comprising the steps of: providing aliquid containing nanoparticles in a first casing part, activating apumping device and pressurising the first casing part, jetting theliquid through a nozzle head towards the inner surface of the casing inthe second casing part in a jet stream, and arranging the layer ofnanoparticles on the inner surface of the casing by the jet stream. 15.A method according to any of claims 12-14, further comprising an initialstep of preparing surfaces of downhole casing parts, such as casings,pipes, tubes, valves, plugs and collars, which may come into contactwith borehole fluids, comprising the steps of: coating an inner surfaceof a casing part with a nanocover material, and mounting the coatedcasing part to the casing.